1. Field of the Invention
The present invention relates to a newly designed power module package, and more particularly to a high-density power module package which is characterized in having the property of high heat dissipation, easiness in fabricating the lead frame, and low production cost.
2. Description of the Prior Art
The conventional power module packages can be classified in three categories, namely:    (1) The first one is shown in FIG. 1A and FIG. 1B, wherein a high heat dissipation substrate 100 made of a high molecular insulation layer and a metal foil layer is prepared as a base substrate. All power pack module circuits and a plurality of chips 101, 102, 103 . . . are fabricated on the surface of the substrate 100. After that the module circuits and lead frames 121, 122, or the chips 101, 102 . . . and the lead frames 121, 122 . . . are electrically connected by wires 111, 113 . . . or by wires 112 . . . respectively utilizing the wire bonding technique.No matter how simple and easy to fabricate, the structure of the above described power module package has the following shortcomings:            1. Density of the power pack module circuits cannot be raised by reason that all the power pack module circuits and the chips are fabricated on the same substrate.        2. The foregoing, shortcoming described in § 1 calls for a larger substrate to compensate for that leads to increasing the production cost.        3. The instantaneous heat conduction ability is poor since heat conduction relies only on the heat dissipation paste applied between the substrate 100 and the heat sink (not shown) which is formed on the outer surface of the substrate 100 for dissipating heat produced by those chips 101, 102 . . . on the power pack module circuits and being conducted to the substrate 100.            (2) The second example is shown in FIG. 2A and FIG. 2B, wherein a metal plate 200 is further attached to the bottom surface of the high heat dissipation substrate 100 for fabricating all the power pack module circuits and attaching chips 101, 102, 103 . . . on the substrate 100. Thereafter, the module circuits and the lead frames 121, 122, or the chips 101, 102 . . . and the lead frames 121, 122 . . . are electrically connected by wires 111, 113 . . . , or wires 112 . . . respectively utilizing the wire bonding technique.
No matter how simple and easy to fabricate, and how advantageous in better heat dissipation by the metal plate 200 attached to the bottom surface of the substrate 100, the above-mentioned structure is unable to be released from the following shortcomings:                1. Density of the power module circuits cannot be raised by reason that all the power module circuits and the chips are fabricated on the same substrate.        2. The foregoing shortcoming described in § 1 calls for a larger substrate for remedy that leads to increasing the production cost.            (3) The third example is shown in FIG. 3A and FIG. 3B, wherein the lead frames 121, 122 . . . are directly patterned on a metal substrate 200 integrally with the power module circuits and the chips 101, 102 . . . are also directly welded to (or using other means) the lead frames. With this structure, there is established a heat conduction route for chips 101, 102 . . . lead frames 121, 122 . . . →thin wall of the package material→metal plate 200→heat sink.
No matter how simple and easy to fabricate, the structure of the above described power module package has the following shortcomings:    1. The density and precision of both circuits and overall structure of the power module package are restricted by reason that the lead frames and overall circuit patterns are integrally formed in one piece.    2. Efficiency of heat dissipation is limited by the fact that heat conduction of chips shall be en route to the metal plate by way of the package material.
In order to solve the above described problems, the present inventor carried out theoretical studies and stimulating experiments. Based on these studies and researches, the present invention came to propose the present invention.